**Preface to "Signal Analysis in Power Systems"**

This issue is devoted to reviews and applications of modern methods of signal processing used to analyze the operation of a power system and evaluate the performance of the system in all aspects. Monitoring capability with data integration, advanced analysis of support system control, and enhanced power security are the key issues discussed in the paper "Analysis of the Power Supply Restoration Time after Failures in Power Transmission Lines". Advanced statistical analysis of the power system is presented in papers "Combined Cluster Analysis and Global Power Quality Indices for the Qualitative Assessment of the Time-Varying Condition of Power Quality in an Electrical Power Network with Distributed Generation" and "The Application of Hierarchical Clustering to Power Quality Measurements in an Electrical Power Network with Distributed Generation", demonstrating the cutting-edge developments in this emerging area. The relatively new concept of virtual power plants, related to ongoing research in cooperation with industrial partners from the energy sector is presented in the paper "A Case Study on Distributed Energy Resources and Energy-Storage Systems in a Virtual Power Plant Concept: Technical Aspects". New concepts of photovoltaic energy forecasting complete the issue with the paper "Forecasting Solar PV Output Using Convolutional Neural Networks with a Sliding Window Algorithm".

> **Zbigniew Leonowicz** *Editor*
